Calendar Control - Calendar closing before date is selected

I have a Calendar Control that isn't working as desired. When the user selects a previous or future month the
calendar will disappear. The user then has to select the dropdown button a second time to see the new month where they can then select the date. What do I need to change in order to not loose visiblity to the calendar until the date in the new month is selected?
<%@ Control Language="VB" AutoEventWireup="false" CodeFile="CalendarControl.ascx.vb" Inherits="CalendarControl" %>

<asp:TextBox id="TextBox1" runat="server"></asp:TextBox>
  <INPUT type="button" value="..." onclick="OnClick()"><br>
<div id="divCalendar" style="DISPLAY: none; POSITION:absolute">
  <asp:Calendar id="Calendar1" runat="server" BorderWidth="2px"
&nb ...